1. Field of the Invention
The invention relates generally to enhanced heat transfer surfaces and a method of and tool for forming enhanced heat transfer surfaces.
2. General Background of the Invention
The invention relates to enhanced heat transfer surfaces that facilitate heat transfer from one side of the surface to the other. Heat transfer surfaces are commonly used in equipment such as, for example, flooded evaporators, falling film evaporators, spray evaporators, absorption chillers, condensers, direct expansion coolers, and single phase coolers and heaters, used in the refrigeration, chemical, petrochemical and food-processing industries. A variety of heat transfer mediums may be used in these applications including, but not limited to, pure water, a water-glycol mixture, any type of refrigerant (such as R-22, R-134a, R-123, etc.), ammonia, petrochemical fluids, and other mixtures.
Some types of heat transfer surfaces work by using the phase change of a liquid to absorb heat. Thus, heat transfer surfaces often incorporate a surface for enhancing boiling or evaporating. It is generally known that the heat transfer performance of a surface can be enhanced by increasing nucleation sites on the boiling surfaces, by inducing agitation near a single-phase heat transfer surface, or by increasing area and surface tension effects on condensation surfaces. One method for enhancing boiling or evaporating is to roughen the heat transfer surface by sintering, radiation-melting or edging methods to form a porous layer thereon. A heat transfer surface having such a porous layer is known to exhibit better heat transfer characteristics than that of a smooth surface. However, the voids or cells formed by the above-mentioned methods are small and impurities contained in the boiling liquid may clog them so that the heat transfer performance of the surface is impaired. Additionally, since the voids or cells formed are non-uniform in size or dimension, the heat transfer performance may vary along the surface. Furthermore, known heat transfer tubes incorporating boiling or evaporating surfaces often require multiple steps or passes with tools to create the final surface.
Tube manufacturers have gone to great expense to experiment with alternative designs including those disclosed in U.S. Pat. No. 4,561,497 to Nakajima et al., U.S. Pat. No. 4,602,681 to Daikoku et al., U.S. Pat. No. 4,606,405 to Nakayama et al., U.S. Pat. No. 4,653,163 to Kuwahara et al., U.S. Pat. No. 4,678,029 to Sasaki et al., U.S. Pat. No. 4,794,984 to Lin and U.S. Pat. No. 5,351,397 to Angeli.
While all of these surface designs aim to improve the heat transfer performance of the surface, there remains a need in the industry to continue to improve upon tube designs by modifying existing designs and creating new designs that enhance heat transfer performance. Additionally, a need also exists to create designs and patterns that can be transferred onto tube surfaces more quickly and cost effectively. As described below, the geometries of the heat transfer surfaces of the invention, as well as tools to form those geometries, have significantly improved heat transfer performance.